The present invention relates to residential electric circuit breakers and more specifically, the present invention is directed to the use of electronics in a residential or miniature circuit breaker such that the current setting of the circuit breaker is modifiable.
In residential circuit breakers, the circuit breakers are typically calibrated to a specific current value. This requires manufacturers, distributors and retailers to build stock circuit breakers calibrated to these unique ratings. Depending upon forecasting and demand changes, this situation results in over inventory or unavailable breakers at each point in the delivery chain.
In contrast, industrial circuit breakers have used the concept of rating plugs with electronic trip units for many years to set the current ratings thereof. By inserting a rating plug, having a discrete resistance value, into a circuit breaker trip unit, the current rating is set for the industrial circuit breaker. Residential circuit breakers do not have the size or cost structure to accept rating plugs and consequently, residential circuit breakers were for practical purposes limited to a predetermined current rating.
Consequently, residential circuit breakers have traditionally used the older thermal magnetic technology which does not have ready methods for changing the current rating of the circuit breaker. The thermal trip characteristic is operative in response to overload current of extended duration which heats a bimetal member, causing movement of the latter, which in turn releases a latch to trip open a set of contacts. The magnetic characteristic is operative in response to a sudden high magnitude current overload condition, and uses the magnetic field generated in a magnetic core to attract typically an armature, which movement releases the latch to open the contacts. As an example, the magnetic type actuation occurs in response to a short circuit wherein the hot line conductor becomes directly connected with ground or neutral, bypassing the load.
In either an industrial or residential environment, it is important to provide a management system which facilitates the efficient use of electricity. In residential circuit breakers, the efficient use of electricity can be obtained by remote control of the residential circuit breaker to remove discretionary loads at the time of peak power usage. In power systems which have experienced a power outage, the return of power can be very difficult due to the large number of electrical loads which will start simultaneously, many with significant inrush current. This problem is known in the art as xe2x80x9ccold load pickupxe2x80x9d and can place serious stress on the electrical system due to any significant inrush which is present during the return of electrical power. Residential circuit breakers have not incorporated load control in the past as a means of alleviating or eliminating the problems associated with a cold load pickup. Past implementations of load control in residential circuit breakers have been xe2x80x9cdumbxe2x80x9d in that an external source of power operates a contact using a conventional solenoid or motor.
It is known to provide remote controlled circuit breakers wherein the breaker contacts are tripped to an open condition by an actuator responding to a control signal. This enables the circuit breaker to additionally perform a switching function and manage a load connected to the breaker, such that the breaker performs the dual functions of overload current protection and load management. A disadvantage of using the breaker contacts to perform a switching relay type function is that the breaker contacts are designed to be able to interrupt high current, not for repeated operation when it is desired to selectively turn the circuit breaker on or off for load control and protection against cold load pickup situations.
In a first embodiment of the present invention, a residential circuit breaker is provided. Preferably, the residential circuit breaker comprises an electronic residential circuit breaker having a selectable current rating which permits the user to easily set and reset the current rating of the circuit breaker depending upon the desired use of the circuit breaker and the environment in which it is to be used. The current rating may be set by a number of different approaches which provide low cost, late point, or post delivery setting of the current rating. In another aspect of the present invention, the residential circuit breaker includes an effective signaling system for load control. A remote device injects a load control signal upon a line and the residential circuit breaker is adapted to receive and process the load control signal. In response to the load control signal, the residential circuit breaker will either open or close a load switch. Thus, after a power outage and the return of power, the connected loads may be staggered with respect to their return to power to eliminate problems which are associated with the simultaneous start-up of a number of loads after the return of power. In yet another aspect of the present invention, a system method for control of electrical loads for utility purposes in a customer""s home over a power line carrier signaling system is presented. Discretionary loads may be taken off-line by signaling the specific residential circuit breaker to which the discretionary load is connected and directing the same to open a load switch to interrupt the flow of current to the discretionary load. Thus, the residential circuit breaker of the present invention permits the discretionary load to be taken off-line during non-trip conditions, where the circuit breaker is otherwise properly functioning.
In yet another aspect of the present invention, the implementation of common power line carrier (PLC) communications in utility revenue meters, circuit breakers, and load centers is presented. This embodiment offers an effective, low cost interface between the electrical infrastructure (utility revenue meter, load center, circuit breakers) and a home automation system for the purpose of load control. The home automation system can be signaled to place deferable loads off line during periods of peak electrical power usage by providing a load control signal to individual electronic residential circuit breakers instructing that the loads connected to these electronic residential circuit breakers be taken off line by opening the load control switch of the electronic residential circuit breaker.
The above-discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings.